Quantitation of cis- and trans-Monounsaturated Fatty Acids in Dairy Products and Cod Liver Oil by Mass Spectrometry in the Selected Ion Monitoring Mode

Abstract

Monounsaturated fatty acids (MUFAs) are important constituents of dietary fats. While cis-configurated isomers belong to the classic fatty acids of food, trans-fatty acids are suspected to pose a risk to human health. In either case, a thorough assessment of both positional and geometrical isomers of MUFAs is an important task in food and life sciences. For this purpose, a method suitable for routine analysis was developed. After lipid extraction and conversion of fatty acids into corresponding fatty acid methyl esters, cis and trans isomers of MUFAs were separated on silver-ion-impregnated cartridges. Fractions containing either cis- or trans-MUFAs were determined by gas chromatography-electron ionization mass spectrometry in the selected ion monitoring (GC/EI-MS-SIM) mode using [M-32](+) as quantification ions and [M-74](+) as well as M(+) as qualifier ions. A total of 14 MUFAs were available as reference standards, but a total of 40 MUFAs (22 cis and 18 trans isomers) were identified with high selectivity in samples of cheese, goat fat, human milk, and cod liver oil. The 18:1 and 16:1 isomers contributed most to both the cis- and trans-MUFAs. Application of internal standards allowed for the quantification of MUFAs only in the food samples. The amount of trans-fatty acids was determined to be 0.9- 4.3 g/100 g, with the lowest levels in human milk fat and the highest levels in Roquefort cheese. After exclusion of oleic acid, the concentrations of trans- and cis-MUFAs were at the same level in samples from ruminants and human milk fat.

Isolation of 6,9,12,15-Hexadecatetraenoic Fatty Acid (16:4n-1) Methyl Ester from Transesterified Fish Oil by HSCCC

“…Positions of double bonds were assigned by GC/EI-MS operated in the full scan mode (using Method B) according to Hauff and Vetter [5]. For instance, m/z 108, m/z 122, m/z 136 and m/z 150 are characteristic for n-3-, n-4-, n-5-and n-6-FAME, while m/z 166, m/z 180, m/z 194, m/z 208 and m/z 222 are indicating the first two double bonds in position D4,7, D5,8, D6,9, D7,10 and D8,11, respectively [26][27][28][29].…”

Fatty acids and polar lipid content of cheese and mould‐contaminated cheese

“…The m/z 79 and m/z 81 (quantification of methyl esters of PUFA) were recorded after elution of 14:0 at 19.3 min. In addition, we recorded the molecular ions [M] þ for the identification of the saturated FAME as well as [M-74] þ and [M-32] þ for the peak assignment and quantification of methyl esters of MUFA according to Hauff and Vetter [12]. Furthermore, the method included m/z 88 and m/z 101 for the determination of the ethyl esters used as internal standards [13,14].…”

“…Furthermore, the method included m/z 88 and m/z 101 for the determination of the ethyl esters used as internal standards [13,14]. Identification and quantification of the IS d 70 -DSPC was based on m/z 77 and m/z 91 [10,12]. Duplicates were analyzed for fatty acids in both NL and PL and mean values will be reported below.…”

“…þ , m/z 284) [12]. However, it could not be excluded that 16:1(7) and 16:1(9) were interfered with 16:1(10tr) and 16:1(11tr).…”

“…Since the trans-isomers are -if any present -of low abundance compared to the cis-isomers, the determination of 16:1(7) and 16:1(9) was considered correct. 18:1 isomers were determined with [M-32] þ (m/z 264) and [M-74] þ (m/z 222) for support instead of m/z 74 [12]. 18:1(10tr) and 18:1(11tr) could not be resolved and only the sum of both isomers could be reported.…”